The invention generally relates to the recovery of aluminum from secondary sources. More specifically, the invention relates to a method for the recovery of aluminum from aluminum dross which forms on the surface of the molten aluminum during aluminum melting operations.
Dross typically contains from 30 to 90% free molten aluminum, depending on the particular processing technique and type of furnace. The remainder consists of a sponge-like network of solid particles containing aluminum oxide and various other oxides, nitrates and carbides which form during the melting operation by reacting with the ambient atmosphere. This network of solid particles is referred to herein as the solids network.
The recovery of aluminum from secondary sources, such as dross, is desirable because the production of aluminum from its primary source, bauxite, is extremely expensive due to the high energy costs involved. Moreover, with energy costs increasing almost daily, such production from secondary sources is becoming even more desirable.
U.S. Pat. No. 4,386,956 to Roth et al discloses a method and apparatus for recovering aluminum from aluminum dross. The apparatus includes a special tray comprising multiple parallel troughs which is positioned adjacent an aluminum melting or holding furnace to collect dross from the furnace. Upon withdrawal of dross from the furnace and collection thereof in the tray, aluminum begins to flow through openings provided in each trough and into a collection pan. As soon as the troughs are filled with dross, the dross is compressed. Such compression causes additional aluminum metal to flow from the dross through openings in the tray and into the collection pan. During the compression operation, the dross is quickly cooled to diminish thermite or oxidation reactions. Compression also causes small droplets of aluminum dispersed throughout the dross to coalesce into large plates at the surface of the dross. The cooled dross material is then typically screened and subjected to other processing techniques to recover aluminum metal remaining in the dross. Compression is provided with a ram which serves as both a heat sink and means to restrict access of oxygen to the aluminum in the dross. The ram is wedge shaped, and it cooperates with a complementary wedge-shaped trough to compress the dross in the trough and force the free aluminum in the dross through the trough openings and into the collection pan. To supplement the cooling effect of the wedge-shaped ram members, Roth discloses that a coolant, generally water, may be circulated through passages or tubes provided in the wedge-shaped ram members.
An apparatus similar to that disclosed in Roth is disclosed in U.S. Pat. No. 4,057,232 to Ross et al which discloses a method and apparatus for separating molten zinc from dross. The apparatus includes dross press comprising a source of power, ram means arranged to be driven from the source, a ladle means having a perforated wall adapted to contain the dross to be pressed, support means for said ram and ladle means, a drive shaft for the ram connected to the source of power, a ram head connected to the drive shaft having a downwardly facing convex external surface which is aligned for concentric interfitting relationship with the ladle means wall which has an upwardly facing concave internal surface complementary in shape to the convex surface of the ram head.
In operation, Ross' ram head is forcibly driven into a mass of dross in the ladle to work the mass to coalesce the vestiges of molten metal in the dross to form droplets and force such through the perforations in the wall in a manner similar to that disclosed in Roth for separating aluminum from its dross.
While the processes disclosed in Roth and Ross ostensibly work as intended, there is always a need for processes and equipment which operate more efficiently and obtain greater yields.
Accordingly, an object of the present invention is to provide an improved press for the recovery of aluminum from aluminum dross.
Another object of the present invention is to provide a dross press which maximizes the recovery of aluminum from aluminum dross by maximizing shear forces within the skim mass.
Another object of the present invention is to provide a dross press for recovering aluminum from aluminum dross which can maximize aluminum recovery without compromising recovery rates.
Yet another object of the present invention is to provide a dross press for recovering aluminum from aluminum dross which inhibits the upward displacement of dross material during compaction to thereby increase the recovery of free aluminum from the dross.
These and other objects will become apparent from the drawings, specification and claims appended hereto.